U.S. Pat. No. 4,743,776, which is assigned to the assignee of the present invention, discloses an integrated drive generator for use in an airframe having a constant speed drive transmission which drives a first shaft rotationally supporting an exciter and main generator and a second shaft rotationally supporting a permanent magnet generator. The permanent magnet generator is axially aligned with the main generator which increases the necessary spacing between the first and second shafts to provide rotary clearance between the main generator and the permanent magnet generator. This increased spacing between the first and second shafts results in gear drives interconnecting a hydraulic pump-motor assembly with an input shaft and the first and second shafts having an increased diameter with a concomitant weight penalty. Additionally, the increased spacing between the first and second shafts enlarges the outside periphery of the housing with a concomitant weight penalty. Furthermore, the overall length of the housing of integrated drive generator is determined by the combined length of the first shaft and a torque converter mounted at one end of the first shaft. The second shaft is connected to a first side of a differential which is part of the constant speed drive transmission. The input shaft from a turbine engine is connected to the second side of the differential. Placement of the permanent magnet generator on the first side of the differential was not a determining factor in the overall length of the housing of the integrated drive generator.
The weight and size of an integrated drive generator is of extreme importance in the design of airframes. Unnecessary weight lessens the overall efficiency of the airframe and its load carrying capability. Increased size either in terms of length or increased peripheral dimension in an integrated drive generator can interfere with the mounting of the integrated drive generator on the propulsion engine as a consequence of interference between the integrated drive generator and the cowling of the engine. Reducing weight reduces overhung moment which lessens the requirement for reinforcing of the mounting flange on the propulsion engine where the integrated drive generator is attached.